Implications of a mixing origin for globular cluster bimodal CN variations

Journal Article · Thu May 01 04:00:00 EDT 1986 · Astron. J.; (United States)

DOI:https://doi.org/10.1086/114089· OSTI ID:6009806

Smith, G H; Bell, R A

New spectroscopic data are presented that reveal that the red giants in the globular cluster NGC 6934 exhibit a bimodal CN distribution, as is common among intermediate-metallicity clusters. Clear evidence for an anticorrelation between the strengths of the lambda3883 CN and the lambda4300 CH bands is found. This observation suggests that the CN-rich NGC 6934 giants have mixed CN(O.)-processed material up into their atmospheres. An analytical formulation is then developed to investigate the behavior of the CN opacity as increasing amounts of CN-processed material are brought into the atmosphere. It is found that in the absence of significant CO formation the CN opacity reaches a maximum at a carbon depletion of approx.0.22 dex, a result that is confirmed by spectrum-synthesis calculations. The advent of significant CO formation in relatively cool (T/sub eff/< or approx. =4000 K) atmospheres causes the CN opacity to peak at smaller carbon depletions. These results are shown to imply that the CN-poor stars, in clusters that exhibit bimodal CN distributions, must be relatively unmixed. It is also found that a bimodal CN distribution within a globular cluster need not imply an underlying bimodal carbon-abundance distribution. In fact a monomodal carbon distribution, with a peak at the low carbon-depletion end, could produce a CN bimodality. The addition of reasonable amounts of both CN and ON-processed material into the atmosphere does not greatly alter the surface carbon depletion at which the CN opacity maximum occurs.

• Research Organization: Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, British Columbia V8X 4M6, Canada
• OSTI ID: 6009806
• Journal Information: Astron. J.; (United States), Journal Name: Astron. J.; (United States) Vol. 91:5; ISSN ANJOA
• Country of Publication: United States
• Language: English

Related Subjects

640102* -- Astrophysics &amp; Cosmology-- Stars &amp; Quasi-Stellar
Radio &amp; X-Ray Sources
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABUNDANCE
ATMOSPHERES
CHEMICAL COMPOSITION
CYANIDES
ELEMENT ABUNDANCE
GIANT STARS
OPACITY
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RED GIANT STARS
STAR CLUSTERS
STARS
STELLAR ATMOSPHERES